When there is a preposition in a relative clause, this usually goes at the end
of the sentence.
Example: That’s the waiter (who) I gave the money to.
This is the film (which) I was telling you about.
That’s the country where he comes from.
Non-defining relative clauses give additional information about people,
things or places. It’s usually between commas. We don’t use that in non-
defining relative clauses but only who (for people), which (for things),
whose (possession), and where (places).
Example: Paul, who started singing at 15, is now very famous.
John’s guitar, which he bought in the sixties, is now worth a lot of money.
London, where I lived 20 years ago, has now got a different skyline.
Jane, whose father is English, can speak Engliosh very well.
In these sentences the relative pronoun CAN NEVER BE OMITTED.